201 research outputs found
ASSESSMENT OF THIGH MUSCLES MECHANICAL CAPACITIES FOLLOWING ACL RECONSTRUCTION USING THE TWO-VELOCITY METHOD
We evaluated the ability of recently proposed two-velocity method to discriminate between thigh muscle mechanical capacities of the involved and the uninvolved leg following ACL reconstruction (ACLR). 15 athletes were tested 4 and 6 months following ACLR. F-V linear relationship parameters (F intercept - F0, V intercept - V0, slope – a, and Pmax) were obtained from line drawn through 60 and 180 °/s data (the \u27two-velocity method\u27). In quadriceps, all parameters revealed between leg differences 4 and 6 months after ACLR. In addition F0 and V0 of the involved leg were higher at 6 than at 4 months after ACLR. In hamstrings, differences between legs were found only for F0 at 4 months. In conclusion, parameter of the two-velocity method could be sensitive enough to detect between-leg differences in muscle F, V, and P producing capacities following ACLR
Mesoscopic Phase Fluctuations: General Phenomenon in Condensed Matter
General conditions for the occurrence of mesoscopic phase fluctuations in
condensed matter are considered. The description of different thermodynamic
phases, which coexist as a mixture of mesoscopically separated regions, is
based on the {\it theory of heterophase fluctuations}. The spaces of states,
typical of the related phases, are characterized by {\it weighted Hilbert
spaces}. Several models illustrate the main features of heterophase condensed
matter.Comment: 23 pages, Latex, no figure
Droplet Fluctuations in the Morphology and Kinetics of Martensites
We derive a coarse grained, free-energy functional which describes droplet
configurations arising on nucleation of a product crystal within a parent. This
involves a new `slow' vacancy mode that lives at the parent-product interface.
A mode-coupling theory suggests that a {\it slow} quench from the parent phase
produces an equilibrium product, while a {\it fast} quench produces a
metastable martensite. In two dimensions, the martensite nuclei grow as
`lens-shaped' strips having alternating twin domains, with well-defined front
velocities. Several empirically known structural and kinetic relations drop out
naturally from our theory.Comment: 4 pages, REVTEX, and 3 .eps figures, compressed and uuencoded,
Submitted to Phys. Rev. Let
The field theory of symmetrical layered electrolytic systems and the thermal Casimir effect
We present a general extension of a field-theoretic approach developed in
earlier papers to the calculation of the free energy of symmetrically layered
electrolytic systems which is based on the Sine-Gordon field theory for the
Coulomb gas. The method is to construct the partition function in terms of the
Feynman evolution kernel in the Euclidean time variable associated with the
coordinate normal to the surfaces defining the layered structure. The theory is
applicable to cylindrical systems and its development is motivated by the
possibility that a static van der Waals or thermal Casimir force could provide
an attractive force stabilising a dielectric tube formed from a lipid bilayer,
an example of which are t-tubules occurring in certain muscle cells. In this
context, we apply the theory to the calculation of the thermal Casimir effect
for a dielectric tube of radius and thickness formed from such a
membrane in water. In a grand canonical approach we find that the leading
contribution to the Casimir energy behaves like which gives
rise to an attractive force which tends to contract the tube radius. We find
that for the case of typical lipid membrane t-tubules. We
conclude that except in the case of a very soft membrane this force is
insufficient to stabilise such tubes against the bending stress which tend to
increase the radius. We briefly discuss the role of lipid membrane reservoir
implicit in the approach and whether its nature in biological systems may
possibly lead to a stabilising mechanism for such lipid tubes.Comment: 28 pages, 2 figures, LaTe
Asymmetries in explosive strength following anterior cruciate ligament reconstruction
Background: Despite its apparent functional importance, there is a general lack of data regarding the time-related changes in explosive strength and the corresponding side-to-side asymmetries in individuals recovering from an ACL reconstruction (ACLR). The present study was designed to assess changes in the maximum and explosive strength of the quadriceps and hamstring muscles in athletes recovering from an ACLR. Methods: Twenty male athletes with an ACL injury completed a standard isometric testing protocol pre-ACLR, four and six months post-ACLR. In addition to the maximum strength (F-max), the explosive strength of quadriceps and hamstrings was assessed through four variables derived from the slope of the force-time curves over various time intervals (REDmax, RED50, RFD150 and RED250). Side-to-side asymmetries were calculated relative to post-ACLR measures of the uninvolved leg ("standard" asymmetries), and relative to pre-ACLR value of the uninvolved leg ("real" asymmetries). Results: Pre-ACLR asymmetries in quadriceps RFD (average 26%) were already larger than in F-max (14%) (p lt 0.05). Six months post-ACLR real asymmetries in RFD variables (33-39%) were larger than the corresponding standard asymmetries (26-28%; p lt 0.01). Average asymmetries in hamstrings' RFD and F-max were 10%, 25% and 15% for pre-ACLR and two post-ACLR sessions, respectively (all p gt 0.05). Conclusions: In addition to the maximum strength, the indices of explosive strength should also be included in monitoring recovery of muscle function following an ACLR. Furthermore, pre-injury/reconstruction values should be used for the post-ACLR side-to-side comparisons, providing a more valid criterion regarding the muscle recovery and readiness for a return to sports
Little groups of irreps of O(3), SO(3), and the infinite axial subgroups
Little groups are enumerated for the irreps and their components in any basis
of O(3) and SO(3) up to rank 9, and for all irreps of C, C, C, D and D. The results are obtained
by a new chain criterion, which distinguishes massive (rotationally
inequivalent) irrep basis functions and allows for multiple branching paths,
and are verified by inspection. These results are relevant to the determination
of the symmetry of a material from its linear and nonlinear optical properties
and to the choices of order parameters for symmetry breaking in liquid
crystals.Comment: 28 pages and 3 figure
Pseudo-boundaries in discontinuous 2-dimensional maps
It is known that Kolmogorov-Arnold-Moser boundaries appear in sufficiently
smooth 2-dimensional area-preserving maps. When such boundaries are destroyed,
they become pseudo-boundaries. We show that pseudo-boundaries can also be found
in discontinuous maps. The origin of these pseudo-boundaries are groups of
chains of islands which separate parts of the phase space and need to be
crossed in order to move between the different sub-spaces. Trajectories,
however, do not easily cross these chains, but tend to propagate along them.
This type of behavior is demonstrated using a ``generalized'' Fermi map.Comment: 4 pages, 4 figures, Revtex, epsf, submitted to Physical Review E (as
a brief report
Numerical observation of non-axisymmetric vesicles in fluid membranes
By means of Surface Evolver (Exp. Math,1,141 1992), a software package of
brute-force energy minimization over a triangulated surface developed by the
geometry center of University of Minnesota, we have numerically searched the
non-axisymmetric shapes under the Helfrich spontaneous curvature (SC) energy
model. We show for the first time there are abundant mechanically stable
non-axisymmetric vesicles in SC model, including regular ones with intrinsic
geometric symmetry and complex irregular ones. We report in this paper several
interesting shapes including a corniculate shape with six corns, a
quadri-concave shape, a shape resembling sickle cells, and a shape resembling
acanthocytes. As far as we know, these shapes have not been theoretically
obtained by any curvature model before. In addition, the role of the
spontaneous curvature in the formation of irregular crenated vesicles has been
studied. The results shows a positive spontaneous curvature may be a necessary
condition to keep an irregular crenated shape being mechanically stable.Comment: RevTex, 14 pages. A hard copy of 8 figures is available on reques
The Effect of Body Size on Countermovement Jump Kinetics in Children aged 7 to 11 years
The purpose this study was to examine the effect of body size oncountermovement jump (CMJ)kinetics in children.Participants(n = 160) aged 7-11 years, divided equally by sex and into primary school year groups(years 3, 4, 5 and 6), each performedone CMJ on aforce platform. The variables bodyweight(BW), peak force (Fmax), in-jump minimum force (IMF), in-jump vertical force range (IFR) and basic rate of force development (BRFD)wereattained from the force-time history and then subsequently scaled to account for body size. A significant age, sex and interaction effect werefound for theabsolutevariables BW, IMF, Fmaxand IFR (P 0.05). No significant age or sex differences were observed for normalised or allometrically scaled values(P > 0.05). The results indicate thatgirls and boys can be grouped together but that body size must be accounted for to enable accurate conclusions to be drawn independent of growth.Bodysizesignificantlyeffects the representation of CMJ kinetic results and therefore, future studies should report both absolute and scaled values.Future research should developan age-appropriate criterion method for children in order to determine processed CMJ variables to further investigate neuromuscular performance of children
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